CIRCADIAN RHYTHM OF LUTEINIZING HORMONE SECRETION IN THE OVARIECTOMIZED RAT IMPLANTED WITH OESTRADIOL

1977 ◽  
Vol 75 (2) ◽  
pp. 251-260 ◽  
Author(s):  
G. CHAZAL ◽  
M. FAUDON ◽  
F. GOGAN ◽  
M. HERY ◽  
C. KORDON ◽  
...  
Keyword(s):  
Circadian Rhythm ◽  
Hormone Secretion ◽  
Plasma Concentrations ◽  
Ovariectomized Rats ◽  
Luteinizing Hormone Secretion ◽  
Implantation Time ◽  
Light Darkness ◽  
Lh Rh ◽  
Lh Releasing Hormone ◽  
Afternoon Peak

Implantation of a solid source of oestradiol into ovariectomized rats produced constant plasma concentrations of the hormone over a long period of time. Under these conditions, LH is released in a circadian pattern with a very marked peak in the afternoon. This circadian rhythm is synchronized to the light–darkness cycle, since it follows exactly a shift in the nycthemeral cycle. The first peak appeared on day 3 after placement of the oestrogen implant; its amplitude was constant from days 3 to 9 after implantation, and decreased gradually during prolonged implantation. The afternoon peak was not correlated with changes in the pituitary sensitivity to exogenous LH releasing hormone (LH-RH), since the LH response to increasing doses of the peptide could be superimposed in the morning and in the afternoon. However, the decreased amplitude of the rhythm observed after more than 9 days of implantation seemed to depend upon a progressive desensitization of the pituitary gland to LH-RH. Pituitary LH content also decreased as a function of implantation time. It is concluded that, under conditions of constant plasma oestradiol concentrations and of constant pituitary sensitivity to LH-RH, a daily activation of the neural trigger releasing pituitary gonadotrophins occurs.

FEEDBACK EFFECT OF OESTROGEN ON LUTEINIZING HORMONE SECRETION BY THE RAT PITUITARY GLAND

1982 ◽  
Vol 92 (3) ◽  
pp. 389-395 ◽  
Author(s):  
TAKASHI HIGUCHI ◽  
MASAZUMI KAWAKAMI
Keyword(s):  
Pituitary Gland ◽  
Hormone Secretion ◽  
Feedback Effect ◽  
Ovariectomized Rats ◽  
Luteinizing Hormone Secretion ◽  
Hypothalamic Area ◽  
Serum Lh ◽  
Lh Rh ◽  
Lh Releasing Hormone ◽  
Lh Secretion

Ovariectomized rats with neural deafferentation at the level of the posterior border of the anterior hypothalamic area (AC rats) were used to re-evaluate the direct feedback effect of oestrogen on the regulation of LH secretion by the pituitary gland. Synthetic LH releasing hormone (LH-RH; 300 ng/kg), injected at 30-min intervals into AC rats with undetectable basal LH, induced pulsatile increase of serum LH concentrations. Oestradiol-17β (5 μg), administered i.v. just before the first LH-RH injection, significantly decreased the LH response to a second injection of LH-RH given 30 min later and to subsequent injections. Maximal inhibition was 58%. Oestradiol-17β (5 μg) given i.v. to control ovariectomized rats decreased serum LH concentrations 40 min after administration; the maximum reduction being 52%. An s.c. injection of oestradiol benzoate (5 μg) increased pituitary responsiveness to LH-RH by the next day in AC rats but decreased serum LH levels in control ovariectomized rats. These results indicate that acute inhibitory and chronic facilitatory effects of oestrogen on LH secretion are exerted at the pituitary gland, without a change in LH-RH secretion. The prolonged inhibitory effect of oestrogen is at the level of the hypothalamus and causes a reduction in LH-RH secretion.

Pulsatile luteinizing hormone secretion in the neonatal male rhesus monkey (Macaca mulatta)

1982 ◽  
Vol 93 (1) ◽  
pp. 71-74 ◽  
Author(s):  
T. M. Plant
Keyword(s):  
Rhesus Monkey ◽  
Hormone Secretion ◽  
Plasma Concentrations ◽  
Light Phase ◽  
Luteinizing Hormone Secretion ◽  
Gonadotrophin Secretion ◽  
Neonatal Stage ◽  
Light Darkness ◽  
Lh Release ◽  
Male Rhesus

In an attempt to establish whether the gonadotrophic hormones are secreted in a pulsatile mode during neonatal development in the rhesus monkey, four infantile males were bilaterally gonadectomized at 1–2 weeks of age. Sequential blood samples were taken 22–36 days later from each animal every 10 min for 3–4 h during the light phase of the 24-h light: darkness cycle and circulating LH concentrations were determined by radioimmunoassay. Plasma concentrations of this gonadotrophin fluctuated dramatically and in an apparently rhythmic fashion with peaks recurring at approximately hourly intervals. These findings indicate that by the neonatal stage of ontogeny the hypothalamic-hypophysial apparatus which governs gonadotrophin secretion in this species is capable of generating a pulsatile or episodic pattern of LH release.

Evidence for the involvement of central conversion of testosterone to oestradiol-17β in the regulation of luteinizing hormone secretion in the cockerel

1983 ◽  
Vol 99 (2) ◽  
pp. 301-310 ◽  
Author(s):  
S. C. Wilson ◽  
P. G. Knight ◽  
F. J. Cunningham
Keyword(s):  
Testosterone Propionate ◽  
Hormone Secretion ◽  
Plasma Concentrations ◽  
Passive Immunization ◽  
Inhibitory Influence ◽  
Luteinizing Hormone Secretion ◽  
Depressive Effect ◽  
Oestradiol Benzoate ◽  
Lh Releasing Hormone ◽  
Lh Secretion

Treatment of intact cockerels with the synthetic antioestrogen tamoxifen caused a significant increase in the plasma concentration of LH. In contrast, passive immunization with an antiserum raised against oestradiol-17β did not lead to an increase in plasma LH. A pronounced depressive effect of injections of 0·1 mg testosterone propionate (TP) or 0·1 mg oestradiol benzoate (OB) on plasma concentrations of LH was prevented by tamoxifen. Furthermore, a pronounced rise in the concentration of LH releasing hormone in the posterior hypothalamus after the injection of cockerels with OB was completely inhibited by tamoxifen. Neither 0·1 nor 0·5 mg androstenedione modified the concentration of LH in plasma. A dose of 0·05 mg TP, which failed to depress the concentration of LH in plasma of intact cockerels, caused a marked fall in plasma LH in castrated cockerels. Tamoxifen itself exhibited weak oestrogen agonist activity in castrated cockerels by causing a reduction in the concentration of LH in plasma. However, tamoxifen prevented any further depressive effect on LH resulting from the injection of TP. These findings suggest that testosterone exerts an inhibitory influence on LH secretion at the central neural level, partially at least, by means of the product of its aromatization, oestradiol-17β.

EFFECT OF 20α-HYDROXYY-4-PREGNEN-3-ONE ON LUTEINIZING HORMONE SECRETION IN THE FEMALE RABBIT

1977 ◽  
Vol 84 (1) ◽  
pp. 45-50 ◽  
Author(s):  
E. V. YoungLai
Keyword(s):  
Luteinizing Hormone ◽  
Hormone Secretion ◽  
Luteinizing Hormone Secretion ◽  
Releasing Hormone ◽  
Female Rabbit ◽  
Oestradiol Benzoate ◽  
Lh Rh ◽  
Lh Releasing Hormone ◽  
Lh Secretion

ABSTRACT Experiments were performed in the rabbit to determine whether 20α-hydroxy-4-pregnen-3-one (20-OHP) can maintain luteinizing hormone (LH) secretion after injections of LH-releasing hormone (LH-RH). Female rabbits were castrated at least 2 weeks prior to investigation. On the day before LH-RH injection they were cannulated and a dose of oestradiol benzoate (OeB), 100 μg/kg, given intramuscularly. LH-RH, 500 ng/kg, was injected as a bolus via the cannula and 20-OHP, 100 μg/kg and 2.5 mg/kg, injected intramuscularly immediately after. Blood was withdrawn at intervals for up to 5½ h after LH-RH injection. LH secretion dropped to pre-stimulation levels within 3 h after LH-RH alone or in combination with 20-OHP. Administration of LH-RH to oestrogen primed intact females also gave a peak of LH which returned to pre-stimulation levels within 3 h. However, mating seemed to maintain LH levels for a greater period of time.

Using a classic paper by I. E. Lawton and N. B. Schwartz to consider the array of factors that control luteinizing hormone production

2007 ◽  
Vol 31 (4) ◽  
pp. 318-322 ◽  
Author(s):  
Angela C. Bauer-Dantoin ◽  
Craig J. Hanke
Keyword(s):  
Circadian Rhythm ◽  
Luteinizing Hormone ◽  
Hormone Secretion ◽  
Historical Context ◽  
Ovariectomized Rats ◽  
Complex Nature ◽  
Pituitary Hormone ◽  
Luteinizing Hormone Secretion ◽  
Hormone Production ◽  
Classic Paper

Two significant benefits derived from reading and discussing classic scientific papers in undergraduate biology courses are 1) providing students with the realistic perspective that science is an ongoing process (rather than a set of inarguable facts) and 2) deepening the students' understanding of physiological processes. A classic paper that is useful in both of these regards is by I. E. Lawton and N. B. Schwartz (A circadian rhythm of luteinizing hormone secretion in ovariectomized rats. Am J Physiol 214: 213–217, 1968). The primary objective of the study is to determine whether tonic (pulsatile) secretion of luteinizing hormone (LH) from the pituitary gland exhibits a circadian rhythm. While this hypothesis seems relatively straightforward, its in vivo investigation necessitates an awareness of the multitude of factors, in addition to the circadian clock, that can influence plasma LH levels (and a consideration of how to control for these factors in the experimental design). Furthermore, discussion of the historical context in which the study was conducted (i.e., before the pulsatile nature of LH secretion had been discovered) provides students with the realistic perspective that science is not a set of facts but rather a systematic series of attempts by scientists to understand reality (a perspective that is difficult to convey using a traditional textbook alone). A review of the historical context in which the study was conducted, and a series of discovery learning questions are included to facilitate classroom discussions and to help deepen students' understanding of the complex nature of pituitary hormone regulation.

Changes in the characteristics of pulsatile luteinizing hormone secretion during the oestrous cycle and after ovariectomy and oestrogen treatment in female rats

1982 ◽  
Vol 94 (2) ◽  
pp. 177-182 ◽  
Author(s):  
Takashi Higuchi ◽  
Masazumi Kawakami
Keyword(s):  
Hormone Secretion ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Oestrous Cycle ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Luteinizing Hormone Secretion ◽  
Oestrogen Treatment ◽  
Serum Lh ◽  
Lh Release

Changes in the characteristics of LH secretory pulses in female rats were determined in different hormonal conditions; during the oestrous cycle and after ovariectomy and oestrogen treatment. The frequency and amplitude of the LH pulses were stable during the oestrous cycle except at oestrus when a pattern could not be discerned because of low LH concentrations. These were significantly lower than those measured during other stages of the cycle. Mean LH concentrations and LH pulse amplitudes increased with time up to 30 days after ovariectomy. The frequency of the LH pulse was unchanged 4 days after ovariectomy when mean LH levels had already increased. The frequency increased 10 days after ovariectomy and then remained stable in spite of a further increase in mean serum LH concentrations. Oestradiol-17β injected into ovariectomized rats caused a decrease in LH pulse amplitude but no change in pulse frequency. One day after treatment with oestradiol benzoate no LH pulse was detectable, probably because the amplitude was too small. A generator of pulsatile LH release is postulated and an oestrogen effect on its function is discussed.

Serotonin-reinstatement of luteinizing hormone surges after loss of positive feedback in ovariectomized rats bearing subcutaneous capsules containing oestrogen

1983 ◽  
Vol 98 (1) ◽  
pp. 7-17 ◽  
Author(s):  
R. F. Walker
Keyword(s):  
Positive Feedback ◽  
Ovariectomized Rats ◽  
Facilitatory Effect ◽  
Serum Progesterone ◽  
Serotonin Content ◽  
Serum Lh ◽  
Serotonin Turnover ◽  
Lh Rh ◽  
Lh Releasing Hormone ◽  
Feedback Responses

In ovariectomized rats treated chronically with oestrogen there is a loss of positive feedback effects on LH secretion. This was not due to depletion of pituitary LH since injection of LH releasing hormone (LH-RH; 50 ng/100 g body wt) caused a significant (P < 0·01) rise in serum LH even after the loss of spontaneous LH surges. However, the magnitude of the increase in serum LH in response to LH-RH was greater (412 ± 41 μg/l) before than after (291 ± 29 μg/l) loss of the LH surges. Excessive blood sampling was also not responsible, since positive feedback responses declined comparably in rats bled daily or once every 3–4 days. Progesterone (0·5 mg s.c.), administered for 5 consecutive days, failed to restore LH surges indicating that deficiency of this steroid after ovariectomy does not cause positive feedback responses to disappear in rats exposed chronically to oestrogen. Moreover regular daily fluctuations in serum progesterone, probably of adrenal origin, occurred before as well as after daily LH surges were lost. Serotonin content and turnover were depressed (P < 0·05) when ovariectomized rats first received the subcutaneous capsules containing oestrogen. This change correlated temporally with the onset of daily LH surges and was eventually lost. After 30 days exposure to oestrogen, serotonin turnover increased (P < 0·01) and positive feedback responses were absent. Catecholamine levels and turnover did not show differential responses to oestrogen and were depressed after acute as well as chronic steroid treatment. p-Chlorophenylalanine (pCPA; 250 mg/kg)+ l-dihydroxyphenylalanine (l-DOPA; 200 mg/kg), which depress serotonin and enhance catecholamine synthesis respectively, failed to reinstate LH surges, but these were restored in 22% of the rats receiving l-DOPA alone. pCPA, followed 2 days later by 5-hydroxytryptophan (5-HTP) at 11.00 h, reinstated LH surges in 88% of rats, and a dose–response curve showed that as little as 4 mg 5-HTP/kg stimulated repetitive LH surges when given with pCPA according to this schedule. However, the administration of α-methyl-p-tyrosine + l-DOPA, an analogous treatment involving catecholamines, was only marginally effective (15%). These findings suggest that perturbations of monoamine metabolism occurring in ovariectomized rats exposed to oestrogen for several weeks contribute to loss of daily LH surges. Since pCPA + 5-HTP restored LH surges most effectively, then positive feedback may disappear as the facilitatory effect of serotonin is lost after chronic oestrogen administration.

Control of follicle-stimulating hormone secretion by steroid-free bovine follicular fluid in the ovariectomized rat

1983 ◽  
Vol 99 (1) ◽  
pp. 1-8 ◽  
Author(s):  
T. R. Koiter ◽  
G. C. J. van der Schaaf-Verdonk ◽  
H. Kuiper ◽  
N. Pols-Valkhof ◽  
G. A. Schuiling
Keyword(s):  
Luteinizing Hormone ◽  
Follicular Fluid ◽  
Hormone Secretion ◽  
Ovariectomized Rats ◽  
Ovariectomized Rat ◽  
Releasing Hormone ◽  
Basal Release ◽  
Lh Release ◽  
Lh Releasing Hormone ◽  
Lh Secretion

The effects of steroid-free bovine follicular fluid (bFF) and sodium phenobarbitone on spontaneous LH releasing hormone (LHRH)-induced secretion of FSH and LH were studied in ovariectomized rats. Luteinizing hormone releasing hormone was administered by infusion to rats anaesthetized with phenobarbitone. Bovine follicular fluid reduced FSH release and synthesis. Luteinizing hormone release remained unaffected after bFF treatment. Phenobarbitone reduced both FSH and LH release. The observed suppressive effects of bFF and phenobarbitone on FSH secretion were additive, suggesting that the basal release of FSH has an LHRH-dependent and an LHRH-independent component. Furthermore, bFF did not affect pituitary responsiveness of LH secretion to LHRH and reduced the responsiveness of FSH secretion only when administered some time before the LHRH challenge. The present observations support the view that in the ovariectomized rat the pituitary gland is the only site of action of inhibin-like activity as present in bFF.

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